1) Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to a tube frame construction for an implement such as a chisel plow or field cultivator.
2) Related Art
Frames for implements such as field cultivators or chisel plows are typically fabricated by welding a series of similar size tubes together. In some frame fabrication methods, such as shown in U.S. Pat. No. 5,190,207, the end of one tube is laser cut to conform to the shape of the adjoining tube. The cut provides a solid connection by wrapping a portion of the cut tube end around the radius of the adjoining tube, and a shortened weld time is achieved. However, the joint can be expensive compared to a straight joint. Straight cut joints sometimes require filler rods during the weld process and often fail to provide the joint strength and integrity necessary for the heavy loading present during field operations of the implement. The frame sections often are made up of numerous short tube lengths with joint strength relying on the weld. If a weld joint is made improperly, the frame can fail. Further, painting operations often require drain holes in the welded tube members and add extra steps to the frame fabrication process. Numerous gussets are usually required, which add extra welding steps and present paint collection and drip problems during painting operations.
In some agricultural frame constructions, the end of one tube is welded to the side of another tube having a greater dimension (i.e., a tube that is 4.times.4 inches is welded to the 5 inch face of a 2.times.5 inch tube). While this joint usually can be formed with a simple fillet weld, the larger wall is prone to flex ("oil canning") due to the loading of the tube welded thereto. The mating tube is attached to the larger wall by a weld joint only, and the wall can deflect under the heavy bending and torsional loads encountered in the field. This deflection greatly reduces fatigue life of the joint. When hinge brackets or the like are attached, the bolts holding the brackets can collapse the wall of the attaching tube. Holding the bolt torque required to maintain joint strength becomes difficult as a result of the wall collapse.
Frame construction often includes clamping or bolting hitch sub-frames to a main frame. The sub-frames transfer draft loads from the towing vehicle to the cross members of the main frame but are expensive to manufacture, ship and assemble. The hitch sub-frame construction often requires expensive connecting points on the main frame. As with any bolted or clamped joint arrangement, the structural integrity and draft load transfer to the cross members is sometimes compromised. A further problem with such an arrangement is that the sub-frame does not extend to the rear of the machine; therefore, adding a rear hitch becomes more difficult.
To provide continuous lateral rank or tube members, some manufacturers use a bridge structure to help transmit loads through the machine. Transversely extending tool-supporting tubes are welded between upper and lower smaller cross section tubes. The bridge structure usually has high weld costs, and many small welds rather than large continuous welds are used. Flare bevel groove welds are necessary and tend to have less structural integrity compared to a fillet weld. The joints tend to crack during combined bending and torsional loading.